Versatile Superconducting Femtovolt Amplifier and Multimeter

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Abstract
We describe the adaption and use of superconducting quantum interference magnetometers for the measurement of voltage, resistance, and inductance. The instrument which we discuss achieves the Nyquist noise limit, about 10−22 W of noise power in a 1‐Hz bandwidth, over a wide range of conditions. This permits resistance measurements down to this power level and a voltage sensitivity of a few femtovolts for low impedance sources. Using a 10‐μA measuring current, inductance changes of 0.1 pH have been measured. We discuss in detail the noise limitations of the device and the design criteria for optimum performance. Circuit and construction designs are presented which allow the device to be used, with minimal changes, for measurements over a wide range of parameters.

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